exporting negative numbers in red colour to an xls file from java

Hello everyone, I want some data to come up in an Excel file from a servlet.The data includes +ve & -ve numbers.While exporting from servlet i need to set the -ve numbers in red colour.I heard its possible. Anybody plz help me ... i am not using any java-excel apis. hre i am attaching the code also....

What kind of data is your "outputdocument"? Ist it CSV? I think your writing a simple text file, not a generic Excel file. So it might be a hint to go the opposite way: Save a Excel table as some sort of text file and look, if it has got some information about colouring in it. A solution might be to use HTML format.